Showing papers on "Substituent published in 2001"

CH/π Attraction: The Origin of Enantioselectivity in Transfer Hydrogenation of Aromatic Carbonyl Compounds Catalyzed by Chiral η6‐Arene‐Ruthenium(II) Complexes

Abstract: The through-space CH/π attraction between the η6 -arene ligand on Ru and the carbonyl aryl substituent (see transition states in picture) plays a key role in the enantioselective transfer hydrogenation of aromatic carbonyl compounds with 2-propanol or formic acid, catalyzed by chiral η6 -arene-RuII complexes.

Hair-dye composition

Abstract: A hair dye composition containing a triazene dissociative direct dye represented by general formula (1): A-N=N-NH-B (1) wherein A and B are each a monocyclic or a bicyclic aromatic heterocyclic group that may have a substituent or a monocyclic or a bicyclic aryl group that may have a substituent and contain none of a carboxy group, a sulfo group and a quaternary ammonium group; and A and B each bind to a triazene-1,3-diyl group represented by -N=N-NH- via a carbon atom within A and B each. A and B may be the same or different.

Bond Dissociation Energies and Radical Stabilization Energies Associated with Substituted Methyl Radicals

Abstract: Bond dissociation energies (BDEs) and radical stabilization energies (RSEs) associated with a series of 22 monosubstituted methyl radicals (•CH2X) have been determined at a variety of levels including, CBS-RAD, G3(MP2)-RAD, RMP2, UB3-LYP and RB3-LYP. In addition, W1′ values were obtained for a subset of 13 of the radicals. The W1′ BDEs and RSEs are generally close to experimental values and lead to the suggestion that a small number of the experimental estimates warrant reexamination. Of the other methods, CBS-RAD and G3(MP2)-RAD produce good BDEs. A cancellation of errors leads to reasonable RSEs being produced from all the methods examined. CBS-RAD, W1′ and G3(MP2)-RAD perform best, while UB3-LYP performs worst. The substituents (X) examined include lone-pair-donors (X = NH2, OH, OCH3, F, PH2, SH, Cl, Br and OCOCH3), π-acceptors (X = BH2, CH=CH2, C≡CH, C6H5, CHO, COOH, COOCH3, CN and NO2) and hyperconjugating groups (CH3, CH2CH3, CF3 and CF2CF3). All substituents other than CF3 and CF2CF3 result in radical stabilization, with the vinyl (CH=CH2), ethynyl (C≡CH) and phenyl (C6H5) groups predicted to give the largest stabilizations of the π-acceptor substituents examined and the NH2 group calculated to provide the greatest stabilization of the lone-pair-donor groups. The substituents investigated in this work stabilize methyl radical centers in three general ways that delocalize the odd electron: π-acceptor groups (unsaturated substituents) delocalize the unpaired electron into the π-system of the substituent, lone-pair-donor groups (heteroatomic substituents) bring about stabilization through a three-electron interaction between a lone pair on the substituent and the unpaired electron at the radical center, while alkyl groups stabilize radicals via a hyperconjugative mechanism. Polyfluoroalkyl substituents are predicted to slightly destabilize a methyl radical center by inductively withdrawing electron density from the electron-deficient radical center.

Hydrogen bond structural group constants.

Abstract: The ability of functional groups to act as hydrogen bond acids and bases can be obtained from either equilibrium constants for 1:1 hydrogen bonding or overall hydrogen bond constants. Either method leads to structural constants for hydrogen bonding that in some way are analogous to substituent constants. Extensive lists of these functional group constants are reported. It is shown that those derived from overall hydrogen bond constants are the more useful in analyses of physicochemical and biochemical properties.

Melanin-concentrating hormone antagonist

Abstract: A melanin-concentrating hormone antagonist which contains a compound represented by the formula or a salt thereof: (I) wherein R represents hydrogen, halogeno, or an optionally substituted cyclic group; X represents a bond or a spacer in which the main chain has one to ten atoms; Y represents a spacer in which the main chain has one to six atoms; ring A represents a benzene ring which may have other substituent(s); ring B represents a five- to nine-membered nitrogenous nonaromatic heterocycle which may have other substituent(s); and R?1 and R2? are the same or different and each represents hydrogen, an optionally substituted hydrocarbon group, or an optionally substituted heterocyclic group, or R?1 and R2? may form an optionally substituted nitrogenous heterocycle in cooperation with the adjacent nitrogen atom and R2 may form an optionally substituted nitrogenous heterocycle in cooperation with the adjacent nitrogen atom and Y. The antagonist is useful as a preventive/remedy for adiposity, etc.

Model reaction for the synthesis of polyhydroxyurethanes from cyclic carbonates with amines: Substituent effect on the reactivity and selectivity of ring‐opening direction in the reaction of five‐membered cyclic carbonates with amine

Abstract: This article focuses on the substituent effect on the reactivity and selectivity of the ring-opening direction in the reaction of five-membered cyclic carbonates with n-hexylamine. The reactivity of the cyclic carbonate and the formation selectivity of the adduct with a secondary hydroxyl group increased as a stronger electron-withdrawing group was introduced at the α-methylene of the cyclic carbonate. These results are discussed on the basis of the stability of intermediates, primary and secondary alcoholate anions, Mulliken charges on carbonyl carbon, and the bond lengths and orders of the OCO single bond. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3678–3685, 2001

Silicon octaphenoxyphthalocyanines: photostability and singlet oxygen quantum yields

Abstract: Photochemical properties of series of axially substituted silicon octaphenoxyphthalocyanines with aryloxy, siloxy, aminoalkoxy, esters of carboxylic acids and sulphonic acid esters residues as axial ligands were studied in dimethylsulfoxide (DMSO) solution. It was found, that under Q-band excitation axial ligands in compounds studied have the propensity to be changed by hydroxyl groups with quantum yields in the range 10 −5 to 10 −2 depending on the nature of the axial ligand. Axial substituent phototransformation was followed by slow photobleaching of dihydroxysilicon octaphenoxyphthalocyanine (photoproduct) in self-sensitized singlet oxygen mediated oxidation of the macrocycle. Singlet oxygen quantum yields were found to be in the range 0.15–0.20 for majority of the phthalocyanines (Pc) studied.

Substituent effects on the physical properties and pKa of phenol

Abstract: Substituent effects on the physical properties and pKa of phenol were studied using density functional theory [B3LYP/6-311G(d,p)] calculations. Substituents alter the physical properties of phenol such as the hydroxyl-group CO and OH bond lengths, the C OH bond angle, and the energy barrier to rotation about the C O bond, and also influence the hydroxyl-group pKa. Except for the rotational barrier, Hammett σ constants showed strong correlation with these property changes. Several quantum chemical parameters, including the natural charge on the phenolic hydrogen Qn(H) and the natural charge on the phenoxide oxygen Qn(O−), the HF/6-311G(d,p) HOMO energy Ehomo, and the proton-transfer energy ΔEprot, outperformed the empirical Hammett constants in modeling changes in the pKa. All of these latter parameters yielded correlation coefficients ∣r∣>0.94 for the pKa. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

Carbamic acid compounds comprising an amide linkage as hdac inhibitors

Abstract: This invention pertains to certain active carbamic acid compounds which inhibit HDAC activity and which have the formula (1) wherein: A is an aryl group; Q1 is an aryl leader group having a backbone of at least 2 carbon atoms; J is an amide linkage selected from: -NR1C(=O)- and -C(=O)NR1-; R1 is an amido substituent; and, Q2 is an acid leader group; and pharmaceutically acceptable salts, solvates, amides, esters, ethers, chemically protected forms, and prodrugs thereof. The present invention also pertains to pharmaceutical compositions comprising such compounds, and the use of such compounds and compositions, both in vitro and in vivo, to inhibit HDAC, and, e.g., to inhibit proliferative conditions, such as cancer and psoriasis.

(Amino)(Aryl)Carbenes: Stable Singlet Carbenes Featuring a Spectator Substituent

Abstract: Several (amino)(aryl)carbenes have been shown to be stable at room temperature in solution and in the solid state. Electroneutrality of the carbene center is ensured by the amino group, which has both π-donor and σ-acceptor electronic character. The aryl group remains a spectator substituent, as shown by single-crystal x-ray analysis and by its chemical behavior. Because only one electron-active substituent is needed, numerous stable carbenes will become accessible, which will open the way for new synthetic developments and applications in various fields.

Understanding the Role of Stereoelectronic Effects in Determining Collagen Stability. 1. A Quantum Mechanical Study of Proline, Hydroxyproline, and Fluoroproline Dipeptide Analogues in Aqueous Solution

Abstract: The importance of local (intraresidue) effects in determining the stability of the collagen triple helix has been investigated with special reference to the role played by hydroxyproline. To this end the dipeptide analogues of L-proline (ProDA), 4(R)-hydroxy-L-proline (HypDA), and 4(R)-fluoro-L-proline (FlpDA) have been studied by means of quantum mechanical ab initio calculations, taking into account solvent effects by the polarizable continuum model (PCM). Our results confirm that the relative stability of up puckerings of the pyrrolidine ring increases with the electronegativity of the 4(R) substituent (X), whereas down puckerings are favored by 4(S) electronegative substituents. Calculations on model compounds show that this effect is due to the interaction between vicinal C-H bonding and C-X antibonding orbitals. Electronegative substituents on the pyrrolidine ring affect cis-trans isomerism around the peptidic bond, with trans isomers stabilized by 4(R) substituents and cis isomers by 4(S) substituents. Also the hydrogen bonding power of the carbonyl moiety following the pyrrolidine ring is affected by 4(R) substituents, but this effect is tuned by the polarity of the embedding medium. Finally, up puckering favors smaller values of the backbone dihedrals phi and psi. All these results strongly support the proposal that the stability of triple helices containing fluorinated or hydroxylated prolines in Y positions is related to the necessity of having up puckerings in those positions.

Cyclopentannulation of 3-Alkylindoles: A Synthesis of a Tetracyclic Subunit of the Kopsane Alkaloids

Abstract: Indoles which bear an alkyl substituent in the 3-position undergo a [3 + 2] annulation reaction when treated with 1,1-cyclopropane diesters in the presence of Yb(OTf)3 resulting in 2,3-cyclopentanoindolines Typically, the reactions are performed at elevated temperatures or at ultrahigh pressures In cases where steric crowding is an issue, ultrahigh pressures are required In reactions involving substituted cyclopropanes, significant regio- and diastereocontrol was observed When the substituent was aromatic or olefinic, the reactions took place at ambient temperature and pressure The applicability of this methodology to the preparation of a key tetracyclic subunit of the kopsane alkaloids was demonstrated

Design, synthesis, and biological evaluation of analogues of the antitumor agent, 2-(4-[(7-chloro-2-quinoxalinyl)oxy]phenoxy)propionic acid (XK469).

Abstract: 2-(4-[(7-Chloro-2-quinoxalinyl)oxy]phenoxy)propionic acid (XK469) is among the most highly and broadly active antitumor agents to have been evaluated in our laboratories and is currently scheduled to enter clinical trials in 2001. The mechanism or mechanisms of action of XK469 remain to be elaborated. Accordingly, an effort was initiated to establish a pharmacophore hypothesis to delineate the requirements of the active site, via a comprehensive program of synthesis of analogues of XK469 and evaluation of the effects of structural modification(s) on solid tumor activity. The strategy formulated chose to dissect the two-dimensional parent structure into three regions-I, ring A of quinoxaline; II, the hydroquinone connector linkage; and III, the lactic acid moiety-to determine the resultant in vitro and in vivo effects of chemical alterations in each region. Neither the A-ring unsubstituted nor the B-ring 3-chloro-regioisomer of XK469 showed antitumor activity. The modulating antitumor effect(s) of substituents of differing electronegativities, located at the several sites comprising the A-ring of region I, were next ascertained. Thus, a halogen substituent, located at the 7-position of a 2-(4-[(2-quinoxalinyl)oxy]phenoxy)propionic acid, generated the most highly and broadly active antitumor agents. A methyl, methoxy, or an azido substituent at this site generated a much less active structure, whereas 5-, 6-, 8-chloro-, 6-, 7-nitro, and 7-amino derivatives all proved to be essentially inactive. When the connector linkage (region II) of 1 was changed from that of a hydroquinone to either a resorcinol or a catechol derivative, all antitumor activity was lost. Of the carboxylic acid derivatives of XK469 (region III), i.e., CONH2, CONHCH3, CON(CH3)2, CONHOH, CONHNH2, CN, or CN4H (tetrazole), only the monomethyl- and N,N-dimethylamides proved to be active.

Synthesis and photophysical and cation-binding properties of mono- and tetranaphthylcalix[4]arenes as highly sensitive and selective fluorescent sensors for sodium.

Abstract: The syntheses and properties of two calixarene-based fluorescent molecular sensors are reported. These comprise tert-butylcalix[4]arene either with one appended fluorophore and three ester groups (Calix-AMN1), or with four appended fluorophores (Calix-AMN4). The fluorophore is 6-acyl-2-methoxynaphthalene (AMN), which contains an electron-donating substituent (methoxy group) conjugated to an electron-withdrawing substituent (carbonyl group); this allows photoinduced charge transfer (PCT) to occur upon excitation. The investigated fluoroionophores thus belong to the family of PCT fluorescent molecular sensors. In addition to the expected red shifts of the absorption and emission spectra upon cation binding, a drastic enhancement of the fluorescence quantum yield—in an “off–on” fashion comparable to that seen in photoinduced electron transfer (PET) molecular sensors—was observed. For Calix-AMN1, it increases from 10−3 for the free ligand to 0.68 for the complex with Ca2+. This exceptional behaviour can be interpreted in terms of the relative locations of the nπ* and ππ* levels, which depend on the charge density of the bound cation. For Calix-AMN4, in addition to the photophysical effects observed for Calix-AMN1, interactions between the chromophores by complexation with some cations have been found in the ground state (hypochromic effect) and in the excited state (excimer formation). Steady-state fluorescence anisotropy measurements for the system Na+⊂Calix-AMN4, show a depolarization effect due to energy transfer (homotransfer) between the fluorophores. Regarding the complexing properties, a high selectivity for Na+ over K+, Li+, Ca2+ and Mg2+ was observed in ethanol and ethanol–water mixtures. The selectivity (Na+/other cations) expressed as the ratio of the stability constants was found to be more than 400.

Polymeric matrix compatibilized naphthopyrans

Abstract: Described are polymeric matrix compatibilized naphthopyran compounds, examples of which are certain 2H-naphtho[1,2-b]pyrans, 3H-naphtho[2,1-b]pyrans and indeno[2,1-f]naphtho[1,2-b]pyrans each having at least one substituent containing terminal and/or pendant groups selected from hydroxyl, carboxyl, sulfo, sulfono, (meth)acryloxy, 2-(methacryloxy)ethylcarbamyl, epoxy or a mixture thereof. Specific substituents are also present on the naphtho, indeno and/or pyrano portions of the compounds. These compounds may be represented by the following graphic formulae: Also described are various substrates that contain or that are coated with such compounds. Optically clear articles such as contact lenses or other plastic transparencies that incorporate the novel naphthopyran compounds or combinations thereof with complementary photochromic compounds, are also described.

Substituent effects on the reactivity of the silicon-carbon double bond.

Abstract: Laser flash photolysis of various organosilicon compounds such as aryl-, vinyl-, and alkynyldisilanes, silacyclobutanes and silacyclobutenes, and alpha-silylketenes and -diazomethanes leads to the formation of reactive silenes which can be detected directly in solution, allowing detailed studies of the kinetics and mechanisms of their reactions with nucleophiles. Over 30 transient silenes have now been studied by these methods, providing the opportunity to systematically assess the effects of substituents at silicon and carbon on the reactivity of the Si=C bond.

Substituent effects on the oxidation and reduction potentials of phenylthiyl radicals in acetonitrile.

Abstract: Oxidation ( ) and reduction potentials ( ) of a series of para-substituted phenylthiyl radicals XC6H4S• generated from the pertinent disulfides or thiophenols have been measured by means of photomodulated voltammetry in acetonitrile. The values of are of particular interest as they give access to the hitherto unknown thermochemistry of short-lived phenylsulfenium cations in solution. Both and decrease as the electron-donating power of the substituent raises, resulting in linear correlations with the Hammett substituent coefficient σ+ with slopes ρ+ of 4.7 and 6.4, respectively. The finding of a larger substituent effect on than is a consequence of a corresponding development in the electron affinities and ionization potentials of XC6H4S• as revealed by quantum-chemical calculations. Solvation energies extracted for XC6H4S+ and XC6H4S- from thermochemical cycles show the expected substituent dependency; i.e., the absolute values of the solvation energies decrease as the charge becomes more delocalized in t...

Cyclization and Self-Organization in Polymerization of Trialkoxysilanes

Abstract: Sol−gel polymerization of organotrialkoxysilanes RSi(OR‘)3 and formation of silsesquioxane (SSQO) structures was followed using SEC, 29Si NMR, and both small- and wide-angle X-ray scattering. Evolution of the SSQO structure is controlled by the competition between intermolecular polycondensation and cyclization. A strong tendency to buildup of polyhedral cyclic oligomersmainly octamer “cages” and larger cagelike structureswas found to grow with increasing size of substituent R. As a result, long substituents prevent gelation of the trifunctional system and increase stability of the SSQO. Because of incompatibility of the polyhedral SSQO framework and pendant organic chains, microphase separation takes place and spontaneous self-organization occurs. A micellar arrangement of compact SSQO domains with a correlation distance corresponding to the size of the substituent is formed, and the ordering is promoted by increasing length of the organic chain. The most organized arrangement was observed with the trial...

The ruthenium-catalyzed addition of β C-H bonds in aldehydes to olefins

Abstract: The addition of a β C–H bond to the formyl group of aldehydes to olefins took place with the aid of Ru(H)2(CO)(PPh3)3 as a catalyst. Several olefins can be used in the catalytic reaction of conjugate enals. The presence of a sterically hindered substituent at the ortho position of benzaldehyde and the presence of an electron donating substituent appear to be important factor in accomplishing the desired coupling reaction.

Mechanism of the addition reaction of alkyl azides to [60]fullerene and the subsequent N2 extrusion to form monoimino-[60]fullerenes.

Abstract: The 1,3-dipolar cycloaddition of methyl azide to C60 and the subsequent nitrogen elimination from the formed triazoline intermediate to yield the aziridine adduct have been studied using semiempirical and density functional methods. The results obtained show that the addition of methyl azide to C60 takes place in the ring junction between two six-membered rings leading to a closed [6,6]-triazoline intermediate with an energy barrier of about 20 kcal mol-1 and an exothermicity of ca. 2 kcal mol-1 at the B3LYP/6-31G**//AM1 level of theory. The subsequent thermal loss of N2 takes place through a stepwise mechanism in which the cleavage of the N−N single bond precedes the breaking of the N−C bond, with a total activation energy of approximately 45 kcal mol-1. The N2 loss occurs simultaneously with the formation of the new N−C bond. During the process, the steric effects of the leaving N2 molecule prevent the addition of the nitrene substituent to the [6,6]-ring junction attacked initially and force the additi...

Synthesis and properties of poly‐(2‐ethynylpyridinium bromide) having propargyl side chains

Abstract: Poly-(2-ethynylpyridinum bromide) (PEPBP) having propargyl side chains was prepared by the direct polymerization of 2-ethynylpyridine and propargyl bromide under mild reaction conditions without any initiator and catalysts. The polymerization proceeded well to give PEPBP with propargyl side chains in relatively high yields. Various spectral data for the polymer structure indicated that the conjugated polymer system having N-propargylpyridinum substituent was formed. This ionic polymer was completely soluble in water, methanol, dimethylformamide, dimethyl sulfoxide, and N,N-dimethylacetamide and well processable into thin homogeneous film. The photoluminescence intensity (λmax = 760 nm) of this polymer increased as the temperature was increased. At 1 KHz and room temperature, this polymer has k′ = 2.9 and σ = 7.3 × 10−10 (S/cm). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3151–3158, 2001